Assessing Heat Risk in a Sub-Saharan African Humid City, Lagos, Nigeria, Using Numerical Modelling and Open-Source Geospatial Socio-Demographic Datasets

Sub-Saharan African cities are faced with heightened heat risk due to climate change and rapid urbanization. This poses particular threat in areas with limited adaptive capacity. However, there is lack of comprehensive heat risk assessment in the region, possibly due to the absence of high-resolution weather data. Here, we propose and demonstrate a methodology for mapping high-risk areas, specifically focusing on Lagos, Nigeria. The approach utilizes advanced numerical modelling techniques and open-source geospatial data.

The urbanized Weather Research and Forecasting (WRF) model is employed to simulate Humidex-based heat stress during a specific heatwave event in March 2020. Open-source high-resolution geospatial dataset were utilized to assess heat exposure and vulnerability. Spatial analysis techniques, including the Moran I test and Optimized Hot Spot Analysis (OHSA), are used to identify spatial clustering patterns and hot spots of heat risk areas. By categorizing the risk layer into hot, cold, and non-significant spots, the critical heat risk zones (CHRZ) are mapped at 99% confidence level.

The CHRZ covers an area of approximately 1110km², primarily consisting of densely populated urban areas, including well-known slums in Lagos. Further investigation indicated that the high-risk zones primarily corresponded to LCZ6, LCZ7 and LCZ3 each constituting 32%, 32%, 15% respectively.